Cold-cathode glow-discharge tube



Nov. 1, 1966 H LL ETAL COLD-CATHODE GLOW-DISCHARGE TUBE Filed Feb. 4,1963 INVENZQRS 0 F. HALL Z. STOCKER BRIAN BY United States Patent3,283,195 COLD-CATHODE GLOW-DISCHARGE TUBE Raymond Frederick Hall,Crawley, and Brian John Stacker, Thornton Heath, England, assignors toNorth American Philips Company, Inc., New York, N.Y., a corporation ofDelaware Filed Feb. 4, 1963, Ser. No. 255,831 Claims priority,application Great Britain, Feb. 14, 1962, 5,666/ 62 3 Claims. (Cl.313185) The invention relates to a glow discharge tube comprising acaesium-activated cathode. It furthermore relates to a method ofproducing a glow discharge tube of this kind.

With the hitherto known glow discharge tubes of the kind comprising acaesium-activated cathode the activating material consisted of somecaesium compound. Thus, it is true, a low value of the maintainingvoltage could be attained, but the lifetime was short. The invention hasfor its object to provide an improvement in this respect.

In a glow discharge tube comprising a caesium-activated cathode, theactivating layer consists, in accordance with the invention, of gold,the caesium-gold alloy CsAu and caesium oxide.

In a method of producing a glow discharge tube comprising acaesium-activated cathode caesium is distilled, in accordance with theinvention, on a gold surface in the tube and is alloyed to the gold,after which oxidation is performed.

In accordance with the invention the gold may be provided in the form ofa gold plate or it may be applied electrolytically to a metal surface orthe gold layer may first be formed in the tube by evaporation on a metalplate, for example of molybdenum or on a molybdenum layer applied byevaporation to the wall, on a nickel layer or on a conductive tin oxidelayer.

The evaporation of the gold layer may be carried out in vacuo or in arare gas under low pressure.

In the method according to the invention the gold and the caesium can bealloyed at a temperature of about 100 C. for such a long time that thephoto emission of the alloyed layer reaches a maximum value.

In accordance with the invention the oxidation of the caesium-gold layercan be performed by causing a discharge to be produced in a rare gastowards the alloyed layer and by allowing gradually such a quantity ofoxygen to enter that the maintaining voltage attains a minimum value,after which the tube is filled with pure rare gas. In accordance withthe invention the oxidation may also take place in vacuo until thethermal emission of the hot layer reaches a maximum at about 100 C. Thetubes according to the invention have maintaining voltages which lieconsiderably below 50 v. not only at the beginning but also after a longoperation. This is contrary to the known tubes, also the initialmaintaining voltage of which lies above 50 v.

The invention will now be described more fully with reference to thedrawing, in which FIGS. 1 and 2 are sectional views of a discharge tubeaccording to the invention parallel to and at right angles to the tubeaxis respectively and FIG. 3 shows the tube in an arrangement suitable-for carrying out the method according to the invention.

Referring to the figures reference numeral 1 designates the glass wallof the discharge tube, having a bottom 2, through which a number ofsupply pins are taken in a vacuum-tight manner; 5 designates amolybdenum cylinder which constitutes the cathode and which is mountedon supporting wires 6. A filament wire 7 is supported by wires 8. Thefilament wire has a thickness of 0.1 mm. and is made of molybdenum witha thin layer of platinum. Around the peak of the V-shaped filament wire7 there is wound a gold wire 9 of a length of 10 mms. and a diameter of0.1 mm. Inside the cathode cylinder 5 there is provided the annularanode 17, which is supported by the wire 10. The glass bulb is providedwith two glass connections 3 and 4 for connection with the caesiumsource and with the exhaust pump and gas-filling system respectively.

As is shown in FIG. 3 a side bulb 12 is sealed in a vacuum-tight mannervia the upper tube to the bulb 11, said side bulb containing a caesiumpellet 13; the exhaust tube 14 leads to the pump and the gas-fillingsystem 16. The bulb 11 is surrounded by a high-frequency coil 15.

The pellet 13 may consist of two parts of silicon and one part ofcaesium bichromate or, for example one part of silicon and one part ofcaesium chrom-ate.

First the tube is degassified in a furnace at 350 C. and after coolingthe filament wire 7 and the gold wire 9 are degassified by passingcurrent at a temperature such that the gold Wire melts and forms apellet. Then the cathode cylinder 5 is degassified by heating itapproximately to red glowing heat by means of high-frequency currents.The caesium pellet is decomposed by means of high-frequency currents, sothat the caesium is precipitated in the bulb 12. Then the cathodecylinder 5 is again degassified. After cooking of the cathode cylinderthe gold is evaporated in vacuo or in neon of a few mms. pressure.Subsequently the neon, if any, is pumped away and the caesium isevaporated from the bulb 12 towards the cathode cylinder 5 by heatingthe bulbs 11 and 12 at a temperature of about C. The caesium alloys withthe gold and this process is continued until the photo-emission of thecathode layer attains approximately the maximum value. The time requiredto this end is about one and a half hours. The bulb 12 is then sealedand the bulb 11 is filled with neon of a pressure of 10 mms. A currentof 10 rna. is passed through the tube and pure oxygen is slowly allowedto enter until the maintaining voltage has reached a minimum value. Thenthe tube is filled with pure neon of a pressure between 5 and 20 mms.

It has been found that test tubes manufactured by said method hadinitially maintaining voltages lying between 31 and 33 v. at a currentof 10 ma, which value increased by a few volts after about 1000 hours.Dependent upon the arrangement of the electrodes the ignition voltagecould initially even attain the low value of 60 v. If the tubes werefilled with helium of a pressure between 3 and 20 mms., the maintainingvoltages were initially 22 to 25 v., the fluctuation being, however,greater than with the neon filling. It is remarkable in this case that,in helium, maintaining voltages are attainable which are lower than theionisation voltage of helium of 24.6 v. Instead of oxidizing the cathodeduring a glow discharge, it may be oxidized in vacuo, in which case theattainment of the maximum of the thermal emission at 100 C. indicatesthe correct degree of oxidation.

From investigations it appeared that the cathode may have free caesium.

What is claimed is: References Cited by the Examiner 1t.l A glowdischarge tube comprising an envelope filled UNITED STATES PATENTS witan ionizable medium and anode and cathode electrodes disposed therein,said cathode comprising a base g g 2? et 3:33 having an activating layerthereon consisting of gold, at 5 2254073 8/1941 i Cesium-gold alloy, andCesium Oxide. James 3 2. A glow discharge tube as claimed in claim 1,where- 2:773:730 12/1956 Lewin 316 8 in the ionizable medium consists ofneon or helium.

3. A glow discharge tube as claimed in claim 2, wherein JAMES LAWRENCE,Primary E a i 10 a 1S i P P Q F and a v. LAFRANCHI, Assistant Examiner.lower voltage 15 required to m-amtaln ionization.

1. A GLOW DISCHARGE TUBE COMPRISING AN ENVELOPE FILLED WITH AN IONIZABLEMEDIUM AND ANODE AND CATHODE ELECTRODES DISPOSED THEREIN, SAID CATHODECOMPRISING A BASE HAVING AN ACTIVATING LAYER THEREON CONSISTING OF GOLD,A CESIUM-GOLD ALLOY, AND CESIUM OXIDE.